1. Field of the Invention
The present invention relates to a connector assembly for an implantable medical device, such as a heart stimulator. accordance with the preamble of the appended independent claims.
2. Description of the Prior Art
U.S. Pat. No. 4,934,366 discloses an implantable medical device in the form of a heart stimulator (pacemaker) in a hermetically sealed enclosure containing electrical circuits, a battery connected to the circuits and a connector part through which the proximal end of an electrode cable can be connected to the heart stimulator and electrically coupled to its circuits. The connector part comprises a tubular sleeve devised as a female connector part with a stepped, cylindrical receptacle, closed at its inner end and open on the end opening onto the exterior of the enclosure, and a middle section between both these channel sections. The diameter of the channel is smallest in its innermost section, largest in its outermost section and intermediate in size in its middle section.
A first, ring-shaped coil spring contact means is disposed in the wall of the inner part of the receptacle channel, and a second ring-shaped coil spring contact means is in the wall of the middle section. Both these contact means are electrically connected to the pacemaker's electrical circuits.
A connector, devised as a male connector with an anterior, narrow, pin-like tip electrode and a ring-electrode, arranged somewhat behind same and with a larger diameter than the diameter of the tip electrode, is devised to interact with the device's tubular female connector. When the male connector is inserted into the female connector, the tip electrode and the ring electrode are brought into electrical contact with the respective coil spring contact means in the tubular connector.
The tip electrode, devised as a cylindrical male connector, is axially separated from the ring electrode by a cylindrical spacer made of an electrically non-conductive material. The receptacle of the tubular connector, devised as a female connector, is also equipped with circular ring seals in the inside walls of the receptacle. These seals are intended to keep the two electrodes of the male connector from coming into electrical contact with each other via body fluid which could seep in through the gap between the exterior of the male connector and the interior of the female connector. The exterior of the male connector behind the ring electrode, which has the greatest diameter, also has encircling, external sealing ribs to seal against the interior of the female connector, thereby preventing the entry of fluid into the aforementioned gap.
Devising the electrically non-conductive spacer section between the tip electrode and a ring electrode at the proximal end of an electrode cable with external, encircling sealing ribs with intermediate grooves is also known.
The device according to U.S. Pat. No. 4,934,366 relates to bipolar connection of an electrode cable to the device's connector part. Since the contact means/electrodes of the interconnectable male and female connector parts therein are axially separated by intermediate spacer sections, a connector is achieved with a relatively great axial length. This length is obviously a disadvantage, since the aim is always to achieve the smallest possible external dimensions for an implantable device of the present kind.
With regard to heart stimulators, the trend is to stimulate the heart using more than two electrodes, implantable in the heart, on the electrode cable. Modification of the aforementioned known type of axial, bipolar electrode connection to accomodate e.g. three or more electrodes should result in an even longer connector part, since more than two coaxial electrodes must then be arranged in axially separate locations with intermediate spacers. The need for effective sealing means (e.g. sealing ribs) to separate the electrodes (i.e. the poles) from each other in the connector at the proximal end of the electrode cable increases to a corresponding degree. Therefore multipolar electrode connection increases both the size and constructional complexity of the sealing means employed to separate the poles from one another.